As a core technology for next-generation optical transport networks, OTN involve technical specifications for the electrical layer and the optical layer and are becoming a mainstream technology used in backbone transport networks. An OTN provides the following features:
Powerful Operation, Administration and Maintenance (OAM);
Powerful Tandem Connection Monitor (TCM) capability and outband Forward Error Correction (FEC) capability; and
Flexible grooming and management of large-capacity services.
In terms of cross-connect, at present the OTN system defines three levels of electrical layer signals: completely standardized Optical Channel Transport Unit k (OTUk), Optical Channel Data Unit-k (ODUk), and Optical Channel Payload Unit-k (OPUk). The OTN system defines three signal bit rate levels: 2.5 Gb/s (k=1), 10 Gb/s (k=2) and 40 Gb/s (k=3).
As shown in FIG. 1, an OTN frame is based on a 4×4080 byte structure (4 rows×4080 columns). The OTN frame structure comprises several areas, including a frame alignment area, an OTUk Overhead (OH) area, an ODUk OH area, an OPUk OH area, a payload area, and a Forward Error Correction (FEC) area:
The frame alignment area includes a Frame Alignment Sequence (FAS) and a Multi-frame Alignment Sequence (MFAS);
The OPUk OH area provides customer service mapping and adaptation management;
The ODUk OH area provides the management and supervision of OTN frames; and
The OTUk OH provides the supervision of transmission sections.
In order to guarantee the transparent transmission of customer data and synchronization & timing signals, OTN cross-connects based on three different bit rate levels of OTUk/ODUk signals. The switching of cross-connects based on ODUk connections is performed by a high-speed asynchronous cross-connect chip. The port bit rate of a high-speed large-capacity asynchronous electrical cross-connect chip available today, however, can usually reach 3.6 Gb/s only. This bit rate supports OTU1/ODU1 signal switching only but does not support hybrid switching of OTUk/ODUk signals of the three different bit rate levels. In addition, during asynchronous cross-connect, OTUk/ODUk signals are not 3R regenerated before passing an asynchronous cross-connect matrix. Therefore, the scale of interconnection of multiple cross-connect chips is restricted and the switching capacity of the OTN system cannot be effectively improved.